1. Field of the Invention
The present invention relates to a recording and/or reproduction apparatus (information disc apparatus) for recording information to an optical disc having a plurality of recording layers or reproducing information from such an optical disc. In particular, the present invention relates to a tracking control technology and a focusing control technology usable for such a recording and/or reproduction apparatus.
2. Description of the Related Art
Conventional optical discs include a recording layer formed of a phase change material, a magneto-optical material, or a colorant, which is used for recording or reproduction of information. Usually, conventional optical discs include a single recording layer. In order to increase the recording capacity, three-dimensional recording or provision of multiple recording layers have been proposed.
With reference to FIG. 8, a conventional representative recording system will be described. An information disc apparatus 700 for recording information to or reproducing information from an optical disc 727 includes a light source 725 and an objective lens 726. The optical disc 727 includes a substrate 728. The substrate 728 has concaves portions 722 and convex portions 723 formed alternately. The optical disc 727 further includes a recording layer 720 provided in close contact with the concave portions 722 and the convex portions 723.
The light source 725 emits a light beam 724. The objective lens 726 converges the light beam 724 to one of the concave portions 722 or one of the convex portions 723 (in the example shown in FIG. 8, one of the concave portions 722). The information disc apparatus 700 detects a servo signal based on the light beam 724 reflected by the concave portion 722 or the convex portion 723, and performs focusing control and tracking control of the light beam 724 based on the servo signal.
With the combination of the information disc apparatus 700 and the optical disc 727, information can be recorded or reproduced with one light beam 724, but the information can be recorded only to one recording layer 720. Three-dimensional recording is impossible.
Referring to FIG. 9, Japanese Laid-Open Publication No. 61-248231 discloses a method for converging two different light beams emitted by two light sources to a guide track of an optical disc and a recording layer, respectively.
An information disc apparatus 800, described in Japanese Laid-Open Publication No. 61-248231, for recording information to or reproducing information from an optical disc 830 includes two light sources 827 and 828, and an objective lens 831. The optical disc 830 includes a substrate 832. The substrate 832 has concaves portions 822 and convex portions 823 formed alternately. The optical disc 830 further includes an intermediate layer 833 provided on the substrate 832 and a recording layer 834 provided on the intermediate layer 833.
The light source 828 emits a light beam 825. The objective lens 831 converges the light beam 825 to the recording layer 834. On the recording layer 834 which is away from the concave portions 822 and the convex portions 823 by a prescribed distance, information is recorded by the light beam 825.
The light source 827 also emits a light beam 824 having a different wavelength from that of the light beam 825. The objective lens 831 converges the light beam 824 to one of the concave portions 822 or one of the convex portions 823 (in the example shown in FIG. 9, one of the convex portions 823). Based on the light beam 824 converged to and reflected by the concave portion 822 or the convex portion 823, the focusing control and tracking control of the light beam 825 are performed.
The information disc apparatus 800 generates a servo signal based on the light beam 824 reflected by the convex portion 823 and performs focusing control and tracking control of the light beam 825 based on the servo signal.
Japanese Laid-Open Publication No. 61-248231 discloses that the range of selection of the material of the recording layer 834 is widened by the method shown in FIG. 9. However, information can be recorded only to one recording layer 834. Japanese Laid-Open Publication No. 61-248231 does not disclose an optical disc having a plurality of recording layers or describe recording of information to the plurality of recording layers.
The information disc apparatus 800 requires two types of light sources in order to emit two light beams having different wavelengths, and thus needs a complicated structure. In addition, it is difficult to maintain the offset amount of the two light beams 824 and 825 at a prescribed value. Therefore, a change in the relative positions of the light paths of the light beams 824 and 825 causes off-tracking or defocusing.
According to one aspect of the invention, a recording and/or reproduction apparatus for an information medium including a substrate having concave and convex portions and a plurality of recording layers is provided. The recording and/or reproduction apparatus includes a light source for emitting a light beam; an optical system for diffracting the light beam emitted by the light source so as to output a first diffracted light beam and a plurality of second diffracted light beams; and a driving section for driving the optical system. The optical system outputs the first diffracted light beam and the plurality of second diffracted light beams, such that when one of the plurality of second diffracted light beams is converged to and reflected by one of the concave and convex portions, the first diffracted light beam is converged to one of the plurality of recording layers. The driving section drives the optical system, such that the one of the plurality of second diffracted light beams is converged to the one of the concave and convex portions.
In one embodiment of the invention, the number of the plurality of second diffracted light beams and the number of the plurality of recording layers are each M, where M is an integer equal to or greater than 2. The first diffracted light beam is converged to an N""th recording layer, among the M recording layers, by the driving section driving the optical system such that an N""th second diffracted light beam, among the M second diffracted light beams, is converged to the one of concave and convex portions, where N is an integer equal to or greater than 1 but equal to or less than M.
In one embodiment of the invention, M is an integer equal to or less than 10.
In one embodiment of the invention, the number of the plurality of second diffracted light beams is equal to the number of the plurality of recording layers.
In one embodiment of the invention, information is recorded to the one of the plurality of recording layers by the first diffracted light beam being converged to the one of the plurality of recording layers.
In one embodiment of the invention, the information medium further includes at least one intermediately layer provided between the plurality of recording layers.
In one embodiment of the invention, a straight line connecting a convergence point of the first diffracted light beam and a convergence point of each of the plurality of second diffracted light beams is substantially vertical to a surface of the plurality of recording layers.
In one embodiment of the invention, the first diffracted light beam has a light amount which is larger than a light amount of each of the plurality of second diffracted light beams.
In one embodiment of the invention, the optical system includes a collimator lens for converting the light beam emitted by the light source to a parallel light beam, an optical element for diffracting the parallel light beam so as to output the first diffracted light beam and the plurality of second diffracted light beams, and an objective lens for converging the first diffracted light beam and the plurality of second diffracted light beams.
In one embodiment of the invention, the recording and/or reproduction apparatus further includes a light detection section for detecting the one of the plurality of second diffracted light beams which has been reflected by the one of the concave and convex portions and generating a first detection signal, and a signal generation section for generating a tracking control signal based on the first detection signal. The driving section drives the optical system based on the tracking control signal.
In one embodiment of the invention, the light detection section detects the first diffracted light beam reflected by the one of the plurality of recording layers and generates a second detection signal. The recording and/or reproduction apparatus further comprises a reproduction signal generation section for generating a reproduction signal based on the second detection signal.
In one embodiment of the invention, the information medium includes a protective plate provided opposite to the substrate with respect to the plurality of recording layers. The first diffracted light beam is converged to the one of the plurality of recording layers after passing through the protective plate.
In one embodiment of the invention, the recording and/or reproduction apparatus further includes a recording section for outputting a recording current for recording information to the plurality of recording layers. The light source emits the light beam based on the recording current.
In one embodiment of the invention, the optical system further includes a splitter for reflecting the first diffracted light beam reflected by the one of the plurality of recording layers and the one of the plurality of second diffracted light beams which has been reflected by the one of the concave and convex portions, and a collecting lens for collecting the first diffracted light beam and the one of the plurality of second diffracted light beams which have been reflected by the splitter.
In one embodiment of the invention, the optical element includes a volume hologram.
In one embodiment of the invention, the optical element includes a fresnel zone plate.
In one embodiment of the invention, the optical system further outputs a plurality of third diffracted light beams, such that when the one of the plurality of second diffracted light beams and one of the plurality of third diffracted light beams are converged to and reflected by the one of the concave and convex portions, the first diffracted light beam is converged to the one of the plurality of recording layers.
In one embodiment of the invention, at least either the concave portions or the convex portions have a pit for representing information.
According to another aspect of the invention, a recording and/or reproduction apparatus for an information medium including a substrate having concave and convex portions and a recording layer having a plurality of recording planes is provided. The recording and/or reproduction apparatus includes a light source for emitting a light beam; an optical system for diffracting the light beam emitted by the light source so as to output a first diffracted light beam and a plurality of second diffracted light beams; and a driving section for driving the optical system. The optical system outputs the first diffracted light beam and the plurality of second diffracted light beams, such that when one of the plurality of second diffracted light beams is converged to and reflected by one of the concave and convex portions, the first diffracted light beam is converged to one of the plurality of recording planes. The driving section drives the optical system, such that the one of the plurality of second diffracted light beams is converged to the one of the concave and convex portions.
In one embodiment of the invention, the number of the plurality of second diffracted light beams and the number of the plurality of recording planes are each M, where M is an integer equal to or greater than 2. The first diffracted light beam is converged to an N""th recording plane, among the M recording planes, by the driving section driving the optical system such that an N""th second diffracted light beam, among the M second diffracted light beams, is converged to the one of concave and convex portions, where N is an integer equal to or greater than 1 but equal to or less than M.
In one embodiment of the invention, M is an integer equal to or less than 10.
In one embodiment of the invention, the number of the plurality of second diffracted light beams is equal to the number of the plurality of recording planes.
In one embodiment of the invention, information is recorded to the one of the plurality of recording planes by the first diffracted light beam being converged to the one of the plurality of recording planes.
In one embodiment of the invention, a straight line connecting a convergence point of the first diffracted light beam and a convergence point of each of the plurality of second diffracted light beams is substantially vertical to the plurality of recording planes.
In one embodiment of the invention, the first diffracted light beam has a light amount which is larger than a light amount of each of the plurality of second diffracted light beams.
In one embodiment of the invention, at least either the concave portions or the convex portions have a pit for representing information.
According to still another aspect of the invention, a recording and/or reproduction apparatus for an information medium including a plurality of substrates and a plurality of recording layers is provided. The plurality of substrates each have concave and convex portions; the plurality of recording layers each have a plurality of recording planes; and at least one of the plurality of substrates is provided between the plurality of recording layers. The recording and/or reproduction apparatus includes a light source for emitting a light beam; an optical system for diffracting the light beam emitted by the light source so as to output a first diffracted light beam and a plurality of second diffracted light beams; and a driving section for driving the optical system. The optical system outputs the first diffracted light beam and the plurality of second diffracted light beams, such that when one of the plurality of second diffracted light beams is converged to and reflected by one of the concave and convex portions of one of the plurality of substrates, the first diffracted light beam is converged to one of the plurality of recording planes of one of the plurality of recording layers. The driving section drives the optical system, such that the one of the plurality of second diffracted light beams is converged to the one of the concave and convex portions.
In one embodiment of the invention, the number of the plurality of second diffracted light beams is M, where M is an integer equal to or greater than 2. The number of the plurality of recording planes of each of the plurality of recording layers is M. The first diffracted light beam is converged to an N""th recording plane, among the M recording planes of the one of the plurality of recording layers, by the driving section driving the optical system such that an N""th second diffracted light beam, among the M second diffracted light beams, is converged to the one of concave and convex portions of the one of the substrates, where N is an integer equal to or greater than 1 but equal to or less than M.
In one embodiment of the invention, M is an integer equal to or less than 10.
In one embodiment of the invention, a total number of the plurality of recording planes is a number obtained by multiplying the number of the plurality of second diffracted light beams by an integer.
In one embodiment of the invention, information is recorded to the one of the plurality of recording planes by the first diffracted light beam being converged to the one of the plurality of recording planes.
In one embodiment of the invention, a straight line connecting a convergence point of the first diffracted light beam and a convergence point of each of the plurality of second diffracted light beams is substantially vertical to the plurality of recording planes.
In one embodiment of the invention, the first diffracted light beam has a light amount which is larger than a light amount of each of the plurality of second diffracted light beams.
In one embodiment of the invention, at least either the concave portions or the convex portions have a pit for representing information.
According to still another aspect of the invention, a recording and/or reproduction apparatus for an information medium including a plurality of substrates and a plurality of recording layers is provided. The plurality of substrates each have concave and convex portions; and at least one of the plurality of substrates is provided between the plurality of recording layers. The recording and/or reproduction apparatus includes a light source for emitting a light beam; an optical system for diffracting the light beam emitted by the light source so as to output a first diffracted light beam and a plurality of second diffracted light beams; and a driving section for driving the optical system. The optical system outputs the first diffracted light beam and the plurality of second diffracted light beams, such that when one of the plurality of second diffracted light beams is converged to and reflected by one of the concave and convex portions of one of the plurality of substrates, the first diffracted light beam is converged to one of the plurality of recording layers. The driving section drives the optical system, such that the one of the plurality of second diffracted light beams is converged to the one of the concave and convex portions.
In one embodiment of the invention, the number of the plurality of second diffracted light beams is M, where M is an integer equal to or greater than 2. The plurality of recording layers are divided into a plurality of groups. The plurality of groups each include M recording layers. The first diffracted light beam is converged to an N""th recording layer, among the M recording planes of one of the plurality of groups, by the driving section driving the optical system such that an N""th second diffracted light beam, among the M second diffracted light beams, is converged to the one of concave and convex portions of the one of the substrates, where N is an integer equal to or greater than 1 but equal to or less than M.
In one embodiment of the invention, M is an integer equal to or less than 10.
In one embodiment of the invention, a total number of the plurality of recording layers is a number obtained by multiplying the number of the plurality of second diffracted light beams by an integer.
In one embodiment of the invention, information is recorded to the one of the plurality of recording layers by the first diffracted light beam being converged to the one of the plurality of recording layers.
In one embodiment of the invention, a straight line connecting a convergence point of the first diffracted light beam and a convergence point of each of the plurality of second diffracted light beams is substantially vertical to a surface of the plurality of recording layers.
In one embodiment of the invention, the first diffracted light beam has a light amount which is larger than a light amount of each of the plurality of second diffracted light beams.
In one embodiment of the invention, at least either the concave portions or the convex portions have a pit for representing information.
Thus, the invention described herein makes possible the advantages of providing (1) a recording and/or reproduction apparatus for performing focusing control and tracking control of a light beam at a high level of precision when used for recording information to or reproducing information from an information disc having a plurality of recording layers or a plurality of recording planes; (2) a recording and/or reproduction apparatus for performing focusing control and tracking control of a light beam at a high level of precision with a simple structure; and (3) a recording and/or reproduction apparatus for avoiding occurrence of off-tracking or defocusing of a light beam.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.